At about thirteen, many girls abruptly become vague; they say things like "I don't know" when asked for an opinion; they no longer raise their hands, they lose a voice. Observers offer several possible reasons for this change. Decline in self-esteem because of verbal criticism from other girls is one, a longing to attract boys is another, and a disappointment at their own perceived devaluation in the culture is a third.
— Robert Bly, The Sibling Society